Investigations are being conducted on the biochemistry of the sensory retina, pigmented epithelium, choroid, and biological fluids in normal and disease states, particularly in animal models of human retinal degenerations and in human retinal diseases. The effects of nutrition, genetic background, and environmental lighting (or darkness) on incidence and progress of chorioretinal degeneration and associated posterior subcapsular cataracts (PSC) are being studied in pink-eyed and black-eyed strains of retinal dystrophic Royal College of Surgeons rats. Factors involved in causing maturation of the cataracts are being elucidated. Nutritional and environmental factors favoring prevention of the cataracts are of special interest. Several diets have been found to prevent mature cataracts, and dark-rearing has been shown to prevent the microscopically-detactable PSC.